Drilling rig and craft



July 22, 1969 B. PERI 3,456,745

DRILLING RIG AND CRAFT Filed April 20, 1967 2 Sheets-Sheet 1 INVENTOR BENJAMIN PERI July 22, 1969 B. PERI 3,456,745

v DRILLING RIG AND CRAFT Filed April 20. 1967 2 Sheets-Sheet 2 INVENTOR BENJAMIN PERI ATTORNEY United States Patent 5 9 Int. Cl. E2111 7/, /02, 19/06 US. Cl. 1755 12 Claims ABSTRACT OF THE DISCLOSURE Drilling rigs are described comprising a tower including a movable pipe clamp for clamping the drilling pipe, mounting means for the clamp permitting lifting and lowering movements thereof in a range of travel substantially below the crown of the tower, and a drive for the clamp. This arrangement greatly increases the stability of the rig and enables the use of smaller and simpler towers. The device is preferably embodied in an off-shore floating craft wherein, the movable pipe clamp operates only in a range of travel below, or the vicinity of, .the center of gravity of the craft. The movable pipe clamp is of a rotatable type including a plurality of wedge-shaped segments, a force ring surrounding the segments and adapted to cam the segments against the pipe, and a lifting ring adapted to lift the force ring.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to drilling rigs and craft, particularly to off-shore floating or semi-submerged drilling rigs in which, according to the invention, the position of the center of gravity of the rig or craft is lowered greatly.

Description of the prior art In currently used drilling rigs, the drilling pipes are raised and lowered by means such as a hook, shackle, sling, or other gripping devices attached to a wire rope passing over a pulley secured to the crown of the rig. The structural strength of the tower, mast, or other member used to support the pulley at the crown of the rig, must be great enough to withstand the stresses caused when extracting the drilling pipes, especially when the drilling pipes are jammed at the well. The general shape of a drilling rig is that of a long and slender tower. Since, in the common case, the extracting force finds reactions at the base and the crown of the drilling tower, the tower itself must be designed so that it is stiff and strong enough to withstand excessive deformation when pipes are extracted. This requirement implies drilling towers that are relatively heavy and expensive to build, which requirement applies to sea and shore installations alike.

For drilling rigs at sea, the problem of craft or drilling rig platform stability is of utmost importance. In the current design of such rigs, the designer tries as much as possible, within economic limitations, to keep the center of gravity of the entire rig as low as possible. With a relatively high center of gravity, the designer is compelled also to raise the metacenter of the craft; i.e. he is compelled to build a platform or craft of large dimensions. Alternatively, weights can be added to the craft to bring down the center of gravity (and thus obtain better stability). However, once again, this will be at the expense of additional craft or platform size. Further, the forces exerted at the crown of the rig tend to introduce turning moments whose result is to decrease the stability of the craft, and may indeed result in the craft capsizing.

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SUMMARY OF THE INVENTION In the present invention, these serious limitations are overcome by the simple expediency of gripping and lifting the drilling pipes from a point much lower than the crown of the rig.

According to the present invention, there is provided a floating drilling rig comprising a floating craft and a tower mounted thereon, characterized in that the rig includes a movable pipe-gripping device for gripping the drilling pipe, mounting means for the movable pipe gripping device permitting lifting and lowering movements thereof no higher than the vicinity of the center of gravity (i.e., preferably below, but could be slightly above) the rig and craft, and power means for applying an extracting force to the movable pipe gripping device to raise and extract the drilling pipe from the medium being drilled.

Further features and advantages of the invention will be apparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS Several embodiments of the invention are illustrated in the following drawings in which:

FIG. 1 is an elevation and partial cross section of an off-shore drilling rig of the semi-submersible type;

FIG. 2 is an elevation and partial cross section of a land-based drilling rig;

FIG. 3 is a cross sectional view of a pipe gripping device of the rotating wedge type; and

FIG. 4 is a cross sectional view of a portion of another type of off-shore drilling rig.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates an off-shore drilling rig of the semisubmersible type in which a vertical tower 8 is attached to a horizontal platform 11 that is floated in the sea 15 by means of a series of bouyant chambers 14. The drilling rig is kept from drifting by means of anchors 16. A series of drilling pipes 1 are coupled together and are either lowered or raised, as the case may be, through the central axis of the rig and tower by means of the combined action of a movable pipe gripping device or clamp 2 and a holding pipe gripping device or clamp 7. As shown in the figure, the upper drilling pipe 1A has been decoupled from the remainder of the drilling pipes 1, and the decoupled pipe is held suspended from the pulley 9 at the crown of the tower by wire rope 19. To take up slack in the free pipe 1A, or for lowering it, use is made of engine 10 whose power need be no greater than that required for overcoming the weight of the decoupled and free pipes 1A in the upper part of tower 8.

The free pipe 1A is freed from the wire rope 19, uncoupled, and stored in pipe storage containers 17. Once the upper part of the tower 8 is cleared of pipe, another section of the drilling pipe 1 can be extracted as follows:

The pipe clamp 2 is lowered to the position shown in the figure. It is to be understood that the clamp 2 can be any suitable type of pipe gripping device, for example, a sling type clamp, hydraulically operated clamp, or any one of a number of pipe gripping devices well known in the art. A preferred clamp is illustrated in FIG. 3. The clamp 2 is then closed so that it grips the pipe 1. The pipe extracting power means or engine 3 is then actuated, and it transmits a pulling force through tackle 5 acting over pulleys 6 attached to the lower structure 4 of the rig. The force of the engine 3 must be suflicient to extract the pipe. Pulling is continued until the extracting clamp 2 approaches holding clamp 7. The extracting engine 3 is stopped. Now the holding clamp 7 is clamped so that it grips the pipe 1. After this, the extracting clamp 2 is released and again dropped down to its lower position by reversing the direction of the extracting engine 3. Once again extracting clamp 2 is closed around pipe 1 and holding clamp 7 is released. The pipe 1 is raised again as described previously. The complete cycle is repeated as many times as is necessary in order that the drilling pipe once again fills the upper part of tower 8. During the lifting operation it is to be noted that the engine 10, wire rope 19 and crown pulley 9 are used together merely to guide and raise the pipe 1A against its own weight only as it is lifted into the tower 8. In other words, the engine 10 is not used for lifting and extracting the pipe 1, and the forces that wire rope 19 must overcome are very much smaller than the extracting force that must be produced by engine 3 and transmitted by pulleys 6 and tackle 5.

It is to be noted that during any of the above operations, the drilling pipe 1 is constantly being rotataed by rotating engine 13 that transmits the power necessary for turning through the shaft and rotating gear 12.

Using the drilling rig of the invention, as described in FIG. 1, certain benefits are obtained: First, because the extracting force for the drilling pipes is being exerted at a point below the center of gravity of the drilling rig, the moments that are produced by the exertion of the extracting force are righting moments; i.e., these moments increase the stability of the floating craft. It means that the whole craft can be made much smaller in all di mensions, and safer under all conditions. The designer need not take special steps to make the rig stable since it is inherently stable. The main design consideration is that the buoyant force of the craft be greater than the sum of the deadweight and pipe extracting force.

Secondly, even if the extracting force is exerted at a point somewhat above the center of gravity of the drilling rig (and this may be the case when drilling is done from certain types of ships, or other craft, or craft in shallow water, for example), the stability of the entire drilling rig is still enhanced greatly by the design of this invention since the extracting forces are not exerted from a point at the crown of the rig, which is the case in current practice. When the extraction force is exerted from a point at the top of the rig, large moments are produced (especially in rough seas) which moments will tend to capsize the rig unless platforms or vessels of very large dimensions are used to produce the stability required.

Thirdly, using this invention, a drilling rig, craft or vessel is easier to anchor since it is much smaller in size than those in current use. This means that it offers much less resistance to wind, waves, currents, and other disturbing forces. Thus, smaller anchoring cables and anchors can be used, or, for the equivalent anchoring elements, the craft of this invention will be easier to fix into position in the sea.

Finally, the drilling tower can be made much smaller and lighter than the towers in current use. This is because the tower need only withstand the forces produced by the weight of the freely suspended pipe in the upper portion of the tower. It is stressed here, that the tower need not in any way withstand the extracting force required for pulling the pipes from below the platform level. Because the tower is lighter it also means that the center of gravity of the whole rig is also lowered. This is an additional element adding to the stability of the whole craft.

Summing up, therefore, the drilling rig of the invention permits great economies in drilling rig construction since, all other factors being equal, it is possible to make the entire craft much smaller in dimension and weight. This means much less materials and construction time is required. Also, power required to propel the craft from place to place is reduced because of smaller size. Finally, anchorage problems are reduced due to the relatively smaller size of the drilling rig.

FIG. 2 illustrates a land-based drilling rig in which a ho zon a platform 26 is anc ored into the g ound 24 with a vertical tower attached to the platform. The vertical tower is made up of two basic sections; the lower section of the tower 8A which is relatively massive, stiff, and strong, and the upper section of the tower 8B which is long and slender, and has much less strength than the lower part of the tower. The drilling rig of FIG. 2 is shown in the position where the drilling pipe 1 has just undergone extraction. The wedge-type holding clamp 7A has been driven so that it grips the drilling pipe. The pipe extraction and lowering clamp 2 has already been released and is shown raised and released in its highest position. Drilling pipe section 1A has been decoupled from the lower pipe 1 and is shown suspended by the turning shaft 27. The turning shaft is generally constructed in a square cross section and is designed to slide through the hydraulic powered rotating gear 23. A turning moment is applied to the gear by a hydraulic motor and shaft 23A that receives hydraulic oil under pressure from a pump 25 through pressure hose 20. The decoupled pipe section 1A and the turning shaft 27 are held vertically by wire rope 19 that goes over the crown pulley 9. The holding engine 10 is used to raise or lower the turning shaft 27 and the drilling pipe 1A. Once decoupled, drilling pipe 1A is disconnected from the turning shaft 27, and it is placed aside.

To continue extraction of the drilling pipe, the pipe extraction and lowering clamp 2 has to be lowered to its lowest position. This clamp is then actuated so that it grips the embedded drilling pipe 1. Next, the turning shaft 27 is lowered and connected to the drilling pipe. The rotating gear 23 is actuated, wedge clamp 7A is released, and now pipe extraction can start by operating pipe extracting engine 3. This will pull on tackle 5 that exerts force through the hoisting block 22 and thus act to raise both the pipe extraction and lowering clamp 2 and the drilling pipe 1 to which it is clamped. Once raised to the position shown in FIG. 2, the cycle can be repeated until all the pipe is extracted. For lowering, the extraction'procedure is reversed. Using the drilling rig of the invention as described in FIG. 2, an important benefit is obtained. Only the lower part of the drilling tower need be built to withstand the relatively large extracting forces required when pulling out the drilling pipe. The upper tower need be built to withstand only the weight of the decoupled pipe and the turning shaft. Thus, this upper tower can be built lightly, using much less material for bracing and structural members, and the tower requires much less time for assembly. Altogether, using the design of this inventionall other factors being equal-because of the lightness of the upper tower, construction and tower placement costs are reduced greatly.

In FIG. 3 a rotating wedge-type pipe clamp is shown in a released position. The clamp includes a plurality of Wedge-shaped segments 30 arranged to surround the pipe 1 to be clamped, the upper ends of the segments being supported by a locking and releasing ring 29. For raising, a lifting force is created by applying pressure to ,hydraulic cylinders 32, in the latter serving as the pipe exrtacting power means. Several of these cylinders are connected to a deck or platform 34 of the rig, and the piston rods 32A pass through the deck or platform 34 and are connected at several points around the periphery of lifting ring 33. With continued application of pressure, the lifting ring will be raised until the lifting ring bearing surface 33A comes into contact with the force rings bearing surface 31A. Since the lifting ring 33 and the force ring 31 are in contact with one another, both will rise upwardly. In this upward travel, the force ring 31 begins to engage the several segmental Wedges 30 and wedging action forces the segmental wedges against the drilling pipe 1 so that the inner surfaces 30A of the segmental wedges come into forceful contact with the outer surface of the drilling pipe 1. Continued application of pressure to cylinders32 will jam the segmental wedges tightly against the drilling pipe. The friction thus produced will be sufficient to withstand the extracting force needed for pulling the drilling pipe, which extracting force will be supplied by power to the hydraulic cylinders 32.

It is to be noted that during the entire process of engaging, and of extracting or lowering drilling pipe, the drilling pipe itself can be turning. For example, in FIG. 1, the pipe is being turned by the rotating gear and shaft 12. Until the rotating wedge-type clamp described above is engaged, none of its parts will turn. However, once the wedges jam, wedges 30 will begin to rotate with respect to ring 29, and force ring 31 will also rotate and will bear against the lifting ring 33.

In the embodiment of the invention shown in FIG. 3, the entire rotating wedge-type clamp is enclosed in a casing or housing 38 attached at the top to the deck 34 and extedning downwardly to the bore hole. Centrally located in the housing is the drilling pipe 1 and the clamp assembly. Drilling-mud is supplied in the direction of arrow 39 to the drilling bit at the end of drilling pipe 1 under pressure. This same mud is then forced, under pressure, in the direction of arrow 28, up the casing pipe 38 until it exits from pipe 28'. The mud is then recirculated to the mud pumps and is returned to the drilling pipe 1. In addition to serving as lubricant for the drilling operation, the drilling mud surrounds the entire clamp assembly and also acts as a lubricant to reduce friction due to the relative rotation between surfaces 31A and 33A.

In order to restrain lifting ring 33 and prevent it from turning, as a consequence of the rotational force that is applied through the force ring 31, the several piston rods 32A are designed with suflicient stiffness as to withstand the stresses set up by the rotational forces. An alternative method for preventing rotation is by attaching a vertical guide 40 to casing 38 and using this to guide lifting ring 33 by means of a slot 41 formed at the periphery of the lifting ring. Thus the entire pipe clamp assembly is free to move up and down, with the wedges jammed, and the drilling pipe turning, but the lifting ring 33 will not turn.

To release the rotating wedge-type pipe clamp, rotation of drill pipe 1 is stopped. Holding wedges 7 of FIG. 1 or 7A of FIG. 2 are driven in to fasten and hold the drilling pipe. Next, hydraulic pressure is applied to ports 36 of hydraulic cylinders 35, and thus ring 29 will be raised and the wedges will be freed.

An alternative to the holding action provided by the simple wedges 7 or 7A mentioned above is to use an additional rotating wedge-type pipe clamp in place of the Wedges 7 or 7A. Now, using two such clamps, it is possible to keep the drilling pipe turning at all times, while the clamping, lifting, releasing, or lowering operations are in progress.

The main and important advantage of the clamp shown in FIG. 3 is that this clamp permits rotation of the drilling pipe even while it is being extracted. In the current state of the art, this combined action insofar as known, has not been practiced in a single clamp positioned between the ends of a rotating pipe.

Another embodiment of the invention is shown in FIG. 4, illustrating the lower portion of another type of off-shore drilling rig of the floating type or of the type fixed to land below water. The remainder of the rig could be as shown in FIG. 1. Use is made of a buoyant chamber serving as the pipe extracting power means to provide the vertical force needed for lifting the drilling pipe out of the bore hole. As shown in FIG. 4, this air chamber is used in combination with one or two rotating Wedge-type pipe clamps. A single rotating wedge-type clamp 2L may be used for lifting, and the holding clamp 2U may be of any conventional clamping form. With two rotating wedge-type pipe clamps, one at 2L and the other at 2U (as shown in FIG. 4) then the pipe drilling process-either drilling in, or extracting pipecan be made a continuous operation, with the drill pipe 1 rotating at all times if that is desired. Further, through the use of an appropriate control circuit, known in the art, the entire drilling or extracting progress can be automated. The operation of the apparatus of the invention of FIG. 4 is as follows:

Drilling pipe 1 is rotating and is in the process of being lifted. Lifting force sufficient to lift the pipe comes about when sufficient compressed air is introduced through hose 46 to the interior 42A of bell 42. As a consequence of the air displacing the water in the bell 42, water level 15A in the bell goes down and a buoyant force is created. The bell 42 applies a lifting force to lower clamp 2L corresponding to the lifting force applied by cylinders 32 in FIG. 3. The lower clamp 2L is positively and initially clamped onto pipe 1 by applying hydraulic fluid to hydraulic cylinders 36L via hoses 47 to prevent slippage in the event that the wedges are not sufficiently jammed when the bell starts to rise. The wedges are jammed and released by the action of hydraulic cylinders 36L as described above with reference to FIG. 3. To prevent the bell 42 from turning, the bell is guided by guide arms 43 sliding over vertical guides 44.

The upper clamp 2U is, during the lifting phase, not clamped, and the drill pipe 1 is free to slide through clamp 2U. The lifting is continued until the bell 42 begins to surface, and raises above the water surface 15. At this point, buoyancy is lost, and the bell will be unable to lift the drill pipe 1 further. Then clamp 2U is actuated by applying pressure to cylinders 36U in order to clamp and hold the drill pipe. The wedges of clamp 2U will begin to turn with the pipe, the pipe being rotated by suitable means such as shown in FIGS. 1 or 2, but the wedges will hold the pipe in its vertical position when, for the next step of the operation, the lower clamp 2L is unclamped. With clamp 2L unclamped, the bell 42 can be lowered under water again by simply letting air out of the bell. It will then lose most of its buoyant force and will sink under its own weight, taking clamp 2L down with it since the clamp is attached rigidly to the top of the bell. The bell 42 and clamp 2L are prevented from descending too far by the end ring 45.

Once the bell is at its lowest position, clamp 2L is once again clamped down, the upper clamp 2U is released, and air is introduced into the bell in order to create a buoyant force great enough to lift the drilling pipe.

By repeating the above described steps, the drilling pipe can be extracted entirely. It should be noted that by using the combination of alifting bell and the rotating wedge-type clamp as described, the drilling pipe can be lowered or raised while the drilling pipe is turning. This has not been accomplished previously in rigs making use of bells for lifting while drilling. A further benefit comes about in that the buoyant force can be accurately adjusted to meet the needs of the drilling operation so that the drill can be effected under an optimal drilling force.

I claim: 7

1. A floating drilling rig comprising a floating craft and a tower mounted thereon, characterized in that the rig includes a movable pipe gripping device for gripping the drilling pipe, mounting means for said movable pipe gripping device permitting lifting and lowering movements thereof in a range of travel no higher than the vicinity of the center of gravity of the rig and craft, and power means for applying an extracting force to said movable pipe gripping device to raise and extract the drilling pipe from the medium being drilled.

2. A drilling rig according to claim 1, further characterized in that it includes means for rotating the drilling pipe while gripped by said movable gripping device.

3. A drilling rig according to claim '1, further characterized in that the upper portion of said tower includes means for supporting an uncoupled pipe.

4. A drilling rig according to claim 1, further characterized in that said power means includes an engine coupled to said movable pipe gripping device to drive same in the lifting and lowering directions.

5. A drilling rig according to claim 1, further characterized in that said drive includes a submerged bell into which air is introduced under pressure to produce a lifting force as a consequence of buoyancy.

6. A drilling rig according to claim 1, further characterized in that said power means includes a hydraulic cylinder coupled to said movable pipe gripping device to apply a lifting force thereto.

7. A drilling rig or craft according to claim 1, further characterized in that said movable pipe gripping device is a rotatable pipe clamp.

8. A drilling rig or craft according to claim 7, further characterized in that it includes a fixed pipe clamp for grasping and holding the drilling pipe.

9. A drilling rig or craft according to claim 7, further characterized in that it includes a second rotatable pipe clamp for grasping and holding the drilling pipe.

10. A drilling rig or craft according to claim 7, further characterized in that said rotatable pipe clamp includes a plurality of wedge-shaped segments arranged to surround the pipe to be clamped, a force ring surrounding said segments and having a cam surface adapted, when the ring is moved vertically, to engage said segments and to cam them against the pipe, and a further ring adapted to engage said force ring to move same vertically, said force ring being rotatable with respect to said further ring.

11. A drilling rig according to claim 10, further characterized in that it includes a casing for said rotatable pipe clamp, the upper end of said casing being attached to the rig and the lower end of said casing extending down to the bore hole, and means for directing drilling mud to flow through said casing and in contact with said rotatable pipe clamp.

12. A drilling rig according to claim 10, further characterized in that the movable pipe clamp includes a releasing ring supporting the upper ends of said segments, and means disposed between said releasing ring and said further ring for effecting the disengagement of the segments from the drilling pipe.

References Cited UNITED STATES PATENTS 2,512,783 6/1950 Tucker 1757 X 3,051,113 8/1962 Swiger 1755 X 3,063,507 11/1962 ONeill et a1 166.5 X 3,158,211 11/1964 McCue et a1 175-85 3,158,212 11/1964 Fanshawe et al. 175--85 3,194,313 7/1965 Fanshawe 175-85 X 3,359,741 12/ 1967 Nelson 175-7 CHARLES E. OCONNELL, Primary Examiner RICHARD E. FAVREAU, Assistant Examiner U.S. Cl. X.R. 17585 

